The present invention relates to systems, methods and devices for sculpturing a laser beam. More particularly, the invention relates to a device located in the path of a laser for blocking or occluding a portion of the laser beam in accordance with a predetermined pattern wherein the portion of the laser beam reaching the target may be varied, and to methods for using such a device. The use of lasers to alter the surface of objects is becoming more important as it becomes apparent that lasers may be precisely focused and the amount of energy transferred to the target can be closely controlled. Lasers have been used in eye surgery, for example, to treat the retinae of diabetic persons. Lasers have also been used by doctors for other precise and delicate eye surgery.
In all of the prior art eye surgery procedures, as well as in other efforts to use laser beam pulses to act on or burn away tissue or other matter, a great concern arises about the ability to control the size and intensity of the beam. In addition, when multiple treatment pulses are intended, precise location and shaping of the beam is desirable.
Until recently, it has not been possible to provide a practical predetermined pattern of treatment where the intensity and duration of the laser pulse is controlled while simultaneously controlling the shape of the laser pulse and the location where the pulse strikes the target. It has been found that the cornea of the eye may be shaped or otherwise treated with a laser beam pulse in a plurality of locations on the eye to achieve a desired result. Until now, however, the ability to control the size, shape and location of the beam has been undesirably limited. It has recently been discovered that predetermined control of the laser beam pulse may be accomplished by passing the laser beam through an iris that is centered on both the axis of the laser beam and on the optical axis of the cornea. By controlling the size of the iris opening and simultaneously controlling the amount of laser energy passing through the iris aperture, the surface curvature of the eye can be changed to correct for myopia or near sightedness. Such a procedure, however, has not found widespread acceptance due to inherent limitations in beam shape and size that an aperture of this type provides. For example, the use of an iris only permits a round, symmetrical alteration in laser beam shape that is not useful for treatment of astigmatism, hyperopia, irregular shapes and even repair of over corrected or inaccurate corrections for myopia.
Treatment for hyperopia by means of a laser necessarily involves the removal of more corneal tissue at the periphery as compared to the center region of the cornea. As a result, the use of only a variable iris-type aperture to alter the shape of a laser beam cannot accomplish this purpose. Teachings in the prior art, such as Yoder, Jr. U.S. Pat. No. 5,219,344, disclose the use of annuli of varying size to effect a greater exposure of peripheral corneal tissue. Notably, however, the methods and apparatus described in Yoder, Jr. also inherently require the use of shapes that are symmetrical about the axis of the laser beam and about the optical axis of the cornea. These methods are therefore inherently limited by the use of aperture discs having a limited number of annuli. Further, the inability to vary the shape of such annuli imposes additional limitations upon the operator as this inability limits the extent to which the cross-sectional shape of the laser beam can be modified.
Similarly, Trokel U.S. Pat. No. 5,108,388 describes a laser surgery method which employs masks having limited numbers of circular or slit-shaped apertures. The inherent limitations in such a method is similar to that of Yoder, Jr. More specifically, while Trokel teaches that any suitable number of openings can be formed in the masks, the cross-sectional shape of the laser beam is nonetheless limited by the specific openings so provided. As a result, the flexibility desired in treating any given curvature malformation or combination of curvature malformations cannot be achieved.
In a more telling example of the limitations of the prior art, the treatment of hyperopia combined with an astigmatism presents an even further complicated problem as tissue not only from the periphery but also along the major axis of the astigmatism must by preferentially removed compared with other regions of the cornea. The methods and apparatus of Yoder, Jr. have significant disadvantages when applied to such a procedure as two different aperture discs, one applicable to hyperopia and one applicable to astigmatism, must be used in conjunction. More importantly, and as above, the aperture discs contain a limited number of apertures from which to select in shaping the cross-sectional area of the laser beam applied to the cornea. As a result, to the extent the procedure can even be performed by the methods and apparatus of Yoder, Jr., inferior results are inevitably obtained.
The teachings of Shimmick, et al. U.S. Pat. No. 5,549,597, while overcoming certain of the disadvantages of Yoder, Jr., is limited in its applicability. Shimmick, et al., which applicants note is not necessarily prior art to the present invention, teaches a device which has variable cylinder blades which are useful in the treatment of astigmatisms. This usefulness is limited, however, as the operation of the cylinder blades cannot provide an effective treatment of hyperopia or an astigmatism combined with hyperopia. Moreover, insofar as the teachings of Shimmick, et al. are silent with respect to either independent movement of the cylinder blades or movement of the cylinder blades asymmetric to the center line of the iris, it fails to overcome many of the limitations found in the prior art.
In view of the deficiencies and disadvantages of the prior art as recognized by applicants, it is an object of the present invention to provide a system, method and device for sculpturing the shape of a laser beam to change the shape of the beam that impacts its intended target.
Another object of this invention is to provide a system, method and device which is useful in sculpturing laser beams into asymmetrical laser beam subportions, including shapes that are not round.
Yet another object of the present invention is to provide a system, method and device capable of shaping a laser beam to permit treatment of astigmatism, hyperopia, irregular shapes and even repair of over corrected or inaccurate corrections for myopia.
It has been unexpectedly found that the systems, methods and devices of the present invention overcome the limitations of the prior art, without adding unnecessary complexity. More specifically, applicants have found that it superior results in the shaping of a cornea can be achieved by using methods and devices which expose a plurality of corneal regions to a plurality of asymmetrical laser beam subportions to affect the shape of said cornea without introducing any substantial asymmetry to the shape of said cornea. Thus, applicants have discovered that by abandoning the teachings of the prior art which rely on laser beam shapes that are substantially symmetrical about the laser beam axis, methods and devices of substantially superior flexibility, economy and practicality can be realized. Accordingly, preferred method aspects of the present invention comprise providing a laser beam having an predefined shape along a beam axis and exposing a plurality of corneal regions to a plurality of asymmetrical laser beam subportions to affect the shape of said cornea without introducing any substantial asymmetry to the shape of said cornea. As used herein, the term xe2x80x9casymmetrical laser beam subportionsxe2x80x9d refers to portions of the laser beam which are not symmetrical about the axis of the laser beam. According to preferred embodiments, the cross sectional shape of the laser beam subportion is substantially defined by a portion of the periphery of said predefined shape, with each of said subportions of said laser beam being produced by occluding a portion of said beam of predefined shape.
A preferred device according to the present invention comprises means for producing a plurality of asymmetrical laser beam subportions from a laser beam traveling along a laser beam axis. Applicants have found that by the use, for example, of a single plate movable in all directions across the path of the laser beam, or a plurality of plates independently operable across the path of the laser beam, the ability to occlude a laser beam to achieve a nearly infinite variety of laser beam subportions can be achieved. An operator of the device can thus occlude the beam to produce a series of laser beam subportions that are highly desirably in the treatment of any curvature malformation or combination of curvature malformations. As a result, the desired corneal curvature can be achieved simply and efficiently, as explained in more detail hereinafter.
The preferred system includes a laser source for directing a laser beam along a laser axis and a target for receiving the laser beam. The device of this invention is located in the laser beam path such that the device is aligned such that any chosen portion of the laser beam is obstructed or occluded.
In a preferred embodiment, the target is the human eye and, more particularly, the cornea of a human eye. The predetermined pattern is intended to shape the cornea as the laser contacts it in controlled pulses at predetermined locations on the cornea, preferably to treat astigmatism, myopia, or hyperopia.
The methods of the present invention comprise a series of sequential steps in which at least two regions of the cornea are each exposed to increasingly larger portions of the laser beam. As the cross-sectional area of the beam is increased, the larger portion of the beam will be understood to include the preceding smaller portion as well thereby exposing the area of the cornea previously exposed to additional laser radiation. In this manner, the entire area of the cornea exposed to laser radiation will be shaped to the desired curvature by gradually varying the amount of exposure across the exposed area.
In the preferred embodiment, two pairs of complimentary regions of the cornea will be sequentially exposed to laser radiation. In each such region, a first part will be exposed to a substantially segmental portion of the beam, and then at least another part will be exposed to a larger substantially segmental portion of the beam in which the larger segmental portion includes the smaller segmental portion. It will be understood that a complementary region of the cornea comprises that region which, when added to the region to which it is complimentary, defines the entire corneal area exposed to laser radiation.
In a more preferred embodiment, each region of the cornea to be treated will be exposed to about forty substantially segmental portions in which each subsequent portion is larger than and includes each preceding portion. It will be understood that as used herein, a substantially segmental shape includes any shape defined by a substantially arcuate boundary and a substantially non-arcuate boundary and that the base of any such shape is understood to be the substantially non-arcuate boundary and the arc of any such shape is understood to be the substantially arcuate boundary. It will be further understood that the arcuate boundary of the beam can include a transition zone through which the cross-sectional area of the beam can expand incrementally from beam portion to beam portion thereby creating a gradual ablation of the periphery of the corneal region so exposed.
According to certain preferred embodiments, the device employed herein includes a housing and frame on which the components that occlude the laser beam are mounted. Control of the device may be accomplished manually but it is preferred that the various components be controlled by a computer into which the desired data has been entered. A keyboard and video monitor are also preferably used in the system to input data and to observe displays of various treatments being performed.
The device preferably includes an iris defining an aperture that is aligned perpendicularly with the axis of the laser beam and, even more preferably, an adjustable iris for adjustable movement of the aperture about the axis. When an adjustable iris is used, the iris is preferably controlled by controlling means receiving instructions from the operator or program of the computer for enlarging or shrinking the aperture as planned. The size of the iris aperture is preferably varied by a gear and electric motor assembly that permits accurate adjustment of the aperture dimension to within the needed tolerances.
Also included in the preferred device is a laser beam modifying means for producing a plurality of asymmetrical laser beam subportions from a laser beam traveling along a laser beam axis. According to preferred embodiments, the modifying means comprises at least one plate movable so as to further obstruct a portion of the laser beam that would otherwise pass through the iris. As used herein, a plate includes a door, gate, shutter or other similar structure which can obstruct or occlude the laser beam. Preferably, the beam modifying means includes a pair of opposed door sections. In one embodiment, the beam modifying means operates the pair of door sections symmetrically about the axis, preferably such that the symmetrical movement of the pair of door sections is simultaneous.
In a highly preferred embodiment, the beam modifying means operates the pair of door sections independently so as to permit movement of one section without regard to movement of the other section. This independent movement and control allows for substantially more flexibility in designing the shape, size and predetermined pattern of the laser beam. The beam modifying means preferably includes a motor for moving the door sections through gears that allow precise movement that is repeatable with respect to a fixed point in space such as the axis of the laser beam to provide maximum control and effectiveness of the present invention. In a preferred embodiment, each of two door sections are operated by a separate motor.
In an alternate preferred embodiment, the beam modifying means includes a single plate which is capable of obstructing any portion including the entirety of the laser beam. In this preferred embodiment, the beam modifying means preferably includes means for moving the plate into positions to occlude substantially any and all portions of the laser beam.
In the preferred embodiment in which the beam modifying means includes two independently movable door sections, the controlling means is also adapted to rotate the device about the laser axis so that the door sections are capable of intercepting any portion of the laser beam as desired. To accomplish this goal, a portion of the device is adapted to be rotated in both the clockwise and counterclockwise directions so as to provide a full circle of laser beam interception or control. In the alternate preferred embodiment in which the beam modifying means includes a single plate, the controlling means need not but may be adapted to rotate the device about the laser axis as the single plate is preferably adapted to obstruct any and all portions of the laser beam without such rotation.